diff -r d686c6876ef6 -r e69274f8d444 mercurial/revlog.py
--- a/mercurial/revlog.py	Mon Sep 03 14:12:45 2012 +0200
+++ b/mercurial/revlog.py	Mon Sep 03 14:19:45 2012 +0200
@@ -607,7 +607,9 @@
         try:
             return self.index.headrevs()
         except AttributeError:
-            pass
+            return self._headrevs()
+
+    def _headrevs(self):
         count = len(self)
         if not count:
             return [nullrev]